document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=727231>Question 727231</A>: <I><SPAN STYLE=\"word-break: break-all;\"> In a study using 13 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is<BR>\n" );
document.write( "A)	a standard normal distribution.<BR>\n" );
document.write( "B)	a t distribution with 12 degrees of freedom.<BR>\n" );
document.write( "C)	a t distribution with 13 degrees of freedom.<BR>\n" );
document.write( "D)	a t distribution with 14 degrees of freedom.<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #445018 by </B><A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><B>jim_thompson5910(35256)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=445018\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The population variance is unknown. So the population standard deviation is also unknown (since variance = (standard deviation)^2)\r<BR>\n" );
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document.write( "So because the the population standard deviation is unknown AND the sample size n is less than 30, this means that you must use the T distribution.\r<BR>\n" );
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document.write( "In this case, you would use a T distribution with degrees of freedom (df) of...\r<BR>\n" );
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document.write( "df = n-1\r<BR>\n" );
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document.write( "df = 13-1\r<BR>\n" );
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document.write( "df = 12\r<BR>\n" );
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document.write( "So the answer is <font color=\"red\">B)	a t distribution with 12 degrees of freedom</font> </SPAN>\n" );
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